Synaptogenesis entails orchestrated changes to the structure of both presynaptic and postsynaptic elements. The present application focuses on two Drosophila genes identified in our mutant screens as having a role in synaptogenesis. The first of these is a member of the 124 family of proteins. Previously considered to be only auxiliary subunits of CaV channels, we have found that they have a novel function in synaptogenesis that is unrelated to their channel functions. Mutants lacking 124-3 from their motorneurons do not form any synaptic boutons at the neuromuscular junction, although axon outgrowth, guidance, and target recognition proceed normally and synaptic vesicles and active zones are present. The defect is selectively in bouton formation. We propose to characterize the defect in these mutants, compare different members of the 124 family for their competence in the two aspects of their function: channel expression and bouton formation, and perform structure/function studies and protein chemistry to probe the mechanism of 124 function at the fly NMJ. The second focus of the application is on the role of importins in mediating synapse to nucleus signaling postsynaptically at the fly NMJ. At this synapse, a novel wg/WNT signaling pathway has been described in which the C-terminus of Frizzled2 receptors is cleaved from the receptor and can translocate to muscle nuclei. We have uncovered two importins (211 and 12) that are required for this C-terminal fragment to enter the nucleus. We propose to clarify the involvement of the importins in this pathway and to use the mutants to determine the developmental significance of this putative signaling pathway. Relevance: The formation of proper synapses is crucial for brain development and defects in this process are likely to account for many forms of neurological developmental delays and cognitive disorders. Synapse to nucleus signaling is known to be important for synaptic plasticity as well, particularly for forms of long-term memory. PUBLIC HEALTH RELEVANCE: This proposal exams two proteins that we have found to have crucial roles in synapse formation. The formation of proper synapses is essential for brain development and defects in this process are likely to account for many forms of neurological developmental delays and cognitive disorders. Synapse to nucleus signaling is known to be important for synaptic plasticity as well, particularly for forms of long-term memory.